1. Field of the Invention
The present invention relates to a wheel used for the cutting, grooving, polishing, grinding and the like of various materials.
2. Description of the Related Art
Ceramic materials such as alumina and silicon nitride have recently been employed as precision parts of electric devices and the like in increasing quantities. Accordingly, there is an increasing demand for high accuracy in the fabrication of these materials, which are difficult to grind.
A metal bond wheel or a resin bond wheel provided with super abrasive grains such as CBN or diamond grains is typically used for the fabrication of such difficult-to-grind materials.
In a metal bond wheel, super abrasive grains are held in a dispersion arrangement or dispersed in a metal bond phase that contains a single kind of metal or alloy. Because the metal bond phase is hard, the metal bond wheel is hardly worn by friction with the work or is hardly chipped, and is therefore excellent in wear resistance. On the other hand, however, a very strong holding force of grains leads to a poor self-edging function, in which super abrasive grains projecting from the surface of the metal bond wheel gradually fall off and are replaced by fresh super abrasive grains. This results in the deterioration of sharpness at the tips of the super abrasive grains, which become dull under the effect of wear.
In a resin bond wheel, super abrasive grains are held in a dispersion arrangement or dispersed in a resin bond phase that contains, for example, a thermosetting resin. The resin bond phase has excellent self-edging properties, permitting a longer duration of a satisfactory sharpness. However, the resin bond wheel suffers from early wear and insufficient strength, prevent high-speed wheel or high-speed cutting.
There is therefore a demand for a composite bond wheel which has both the excellent wear resistance of a metal bond phase and the excellent self-edging properties of a resin bond phase, in a good balance.
To cope with such a demand, various improvements have been suggested over the conventional metal bond wheel and the conventional resin bond wheel.
The aforementioned improvements in the conventional art will now be described with reference to FIGS. 4 and 5.
FIG. 4 is an enlarged sectional view illustrating a typical metal bond wheel. In this metal bond wheel 1, super abrasive grains 3 including, for example, diamond abrasive grains are held in a dispersion arrangement by a metal phase 4 including, for example, Ni in a grain layer 2. A phenol resin, for example, is baked onto the surface of the metal phase 4 and is covered with a resin phase 5, and the super abrasive grains 3 are exposed on the resin phase 5.
FIG. 5 is an enlarged sectional view illustrating a typical resin bond wheel. In this resin bond wheel 6, super abrasive grains 8 including, for example, diamond abrasive grains are held in a dispersion arrangement in a resin bond phase 9 including, for example, a resin such as a polyimide resin in a grain layer 7. In the resin bond phase 9, mixed metal powder including, for example, copper and tin serving as a metal filler 10 is added in a dispersion arrangement.
In the metal bond wheel 1, described above, having a soft resin phase 5 formed through baking onto the surface of the metal phase 4, the resin phase 5 is worn out by friction with the work or by chipping, and at the point when the wear of the super abrasive grains 3 causes a deterioration of sharpness, grains fall off the resin phase 5, and self-edging functions cause fresh super abrasive grains 3 to project from the surface of resin phase 5.
The resin phase 5 is provided, however, only on the surface of the metal phase 4. If wear of the resin phase 5 proceeds and the resin phase 5 disappears completely, there would remain only the metal phase 4 holding the super abrasive grains 3 with the metal alone, thus leading to a deterioration of the self-edging properties. Therefore, when the metal bond wheel 1 is used for the fabrication of a hard and brittle material, for example, the resin phase 5 disappears at an early stage, resulting in the deterioration of the finished surface quality of the workplace.
In the resin bond wheel 6 described above, the particles of metal powder added as the metal filler 10 to the resin bond phase 9 are individually isolated, and no bonding state is formed between metal particles. This resin bond wheel 6 is therefore poor in improving the wear resistance of the resin bond phase 9 against friction with the work or chipping, and it has been heretofore impossible to prevent rapid wear, which is a defect of the resin bond wheel.